Continuous rod is a long string of hardened, solid steel rod. The continuous rod was developed nearly 30 years ago for reciprocating pump applications where multiple-coupled sucker rods were typically used. Unlike separate sucker rods that couple together every 25 or 30-ft, the continuous rod only requires couplings at the top and bottom of the rod string. An early example of a unitary steel sucker rod string is disclosed in U.S. Pat. No. 3,923,469, which is incorporated herein by reference.
Today, operators can use continuous rod, such the COROD® brand of continuous sucker rod, for artificial lift systems, pump applications, and other well operations. (COROD is a registered trademark of Weatherford/Lamb, Inc.) The continuous rod (also called continuous sucker rod or coiled sucker rod) can be manufactured to almost any desired length. The rod is typically heat treated to a tensile strength of about 110-ksi, which corresponds to a Rockwell hardness value of about 26-HRc. Any hardness value above this may result in increased corrosion in an H2S environment.
The cross-section of the rod can be round or elliptical and can range in size from about 12/16-in to about 18/16-in. Both the round and elliptical rods can be used for reciprocating rod-pumping applications, but the round rod is better suited for rotary-type rod-pumping applications. Today, round rod is a necessary component to meet the high torsional needs of progressing cavity pumps. In fact, most of the continuous rod produced today has a round cross-section, and the demand for larger diameter rod continues to increase.
Due to its length, the continuous rod is coiled for storage and transport on a spool or reel. An early example is such a reel is disclosed in U.S. Pat. No. 3,504,866, which is incorporated herein by reference. For purposes of discussion, FIG. 1A reproduces a conventional transport reel 10 used for storing and transporting coiled rod. The reel 10 has a hub 12 with arms 14 extending outward therefrom. Bars 16/18 connected to each of the arms 14 extend upwards, and wire rings 22/24/26/28 interconnect the bars 16/18 together. A length of continuous rod (not shown) can be coiled in (and uncoiled from) the bars 16/18 as the reel 10 is rotated about the hub 12. This conventional reel 10 has a diameter of 18-ft, which is the standard throughout the industry.
As noted previously, continuous rod was originally developed to operate reciprocating downhole pumps. Because the continuous rod only needed to support reciprocating motion for these pumps, the rod did not require a specific cross-section. Therefore, manufacturers chose an elliptical cross-section for the rod, such as disclosed in U.S. Pat. No. 3,923,469. This elliptical cross-section ensured that the rod could be easily coiled on a reel without excessive bending stresses and then straighten itself after it was uncoiled.
The elliptical rod was used for a long time exclusively in North America and mainly in Canada. Accordingly, manufacturers configured a reel with an 18-ft (216-in) diameter based on Canada's transport regulations to store and transport rod. This 18-ft diameter reel, such as disclosed in U.S. Pat. No. 3,504,866, was large enough for coiling the rod on the reel 10 without permanent deformation, but was small enough to facilitate transporting the reel 10 under Canada's regulations.
Later, downhole rotary pumps were developed. Because these pumps are operated by rotation, the continuous rod used for these pumps needed a more round cross-section to handle torque. Naturally, manufacturers began storing and transporting this round rod on the 18-ft diameter reels 10 already existing in inventory. When coiled on these existing reels 10, however, the round rod experienced much higher bending stresses, and the outer skin of the round rod tended to yield. For example, round rod with a 1-in diameter coiled in one of these 18-ft diameter reels 10 can be significantly stressed and permanently bent because surface bending stresses can be as high as 138-ksi. Operators found that the yielding of the round rod coiled in the 18-ft diameter reel did not apparently affect the operation of the rod once deployed and straightened for use with a downhole rotary pump. Yet, further reduction in the 18-ft diameter of the conventional reels has not been sought or promoted due to the problems with yielding stress. Accordingly, the current amount of yielding of the round rod has become an expected consequence of coiling the round rod on the 18-ft diameter reels 10, and the round cross-section rod has been used with the 18-ft diameter reels 10 for many years.
Despite its usefulness and industry acceptance, storing and transporting continuous rod on the existing 18-ft diameter reels 10 can be expensive and time-consuming. Depending on where the rod is to be used, the reel 10 with the coiled rod may be transported on any number of trucks and ships and may pass through several areas of the world with different shipping and transportation requirements. In most places and especially Canada, the current 18-ft diameter used for the reels 10 limits the transportation of the continuous rod to truck mounted transportation. As expected, the size and weight limitations for truck-mounted transportation can be significant.
As one example, FIG. 1B shows an end view of a truck trailer 30 carrying a conventional 18-ft diameter reel 10 on a support 40. The trailer 30 can have one or more such reels 10 disposed along its length and can be hauled by a truck, a dedicated vehicle, etc. The reels 10 carry the continuous rod, and the trailer 30 transports the reels 10 from a manufacturing facility to a well site for installation or to a ship for international or overseas shipment. The traveling space for the trailer 30 and reels 10 viewed from the end is limited to about 12-ft by 15-ft. In this way, the reels 10 with their 18-ft diameter are built as large as possible to just meet the dimensional limits defined by Canada's transport regulations so they can be transported with less restriction.
Unfortunately, rail transportation of the 18-ft diameter reels 10 is not possible due to their size. In addition, the reels 10 must be shipped as bulk freight for overseas shipments, requiring special handling procedures and equipment. As expected, any long distance transport of these reels 10 can be very expensive, and the difficulties and expense involved in transporting the rod has limited its application and use in the industry.
In addition, the conventional reel 10 shipped with the coiled rod is a substantial inventory item. Therefore, the empty reel 10 must be returned to a facility for reuse. As expected, returning the empty reel 10 from a distant location to the manufacturing facility can still cost a considerable amount.
All of the required costs and travel time involved in transporting rod on the conventional 18-ft diameter reel 10 have been recognized in the industry for some time, but have simply become accepted. In fact, one recently recognized solution in the industry to overcome the problems with transporting continuous rod has sought to avoid the transportation issue entirely. For example, U.S. Pat. No. 6,481,082 proposes a technique for making continuous rod directly at the well site by welding individual, 40-ft lengths of straight round bar together on location to form the desired rod. In this way, the rod does not need to be manufactured at a facility and transported on a reel to the work site. Although this solution avoids the issue of transporting the continuous rod, it creates potentially new difficulties at the work site.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.